In current large-scale networks, information flows through a series of nodes/network elements in the network from one location or site to another. FIG. 1A illustrates a related art system 100 that has an east 110 and west 140 terminal. The east 110 and west 140 terminals communicate via lines (e.g., optical fiber pairs) that run between the terminal, as illustrated (e.g., lines 152-156 and 162-166). east 110 and west 140 terminals can be located a significant distance apart. Accordingly, line amplifier nodes (e.g., 120, 130) can be interposed between the terminals (e.g., every 40-80 kilometers) to compensate for the signal loss in the transmission medium (e.g., optical fiber) by amplifying the signal. Additionally, associated dispersion compensation modules (e.g., DCMs 122, 128, 132 and 138) can be added to correct for the signal degradation caused by the transmission medium (e.g., dispersion in the optical fibers). Further, to increase the bandwidth available each east and west line can have a plurality of channels communicated on separate wavelengths in different bands (e.g., red and blue), as is known in the art. Generally, the red band can be considered to be a contiguous band of longer wavelengths and the blue band is a contiguous band of shorter wavelengths, within the bandwidth supported by an optical amplifier.
The amplification gain at a given node should typically correspond to the losses incurred in the upstream line. Likewise, the dispersion compensation typically can correspond to the fiber dispersion in the upstream line. Accordingly, methods and systems for measuring the fiber loss and compensating for loss and for compensating for the fiber dispersion are desired in optical communication systems.
In addition to line amplifier nodes, add/drop nodes can be interposed between terminals to allow for the adding or dropping of signals from the lines, as is known in the art. FIG. 1B illustrates a related art optical add/drop multiplexer. Each line (e.g., west to east line 170, east to west line 180) is coupled to an optical line amplifier (OLA) 171, 181, which includes amplifiers and a dispersion compensating fiber (DCF) as is known in the art. The output of the OLA is coupled to a drop element 172, 182. A reconfigurable blocking filter (RBF) 173, 183 is coupled between the drop element 172, 182 and an add element 174, 184. The add element 174, 184 is coupled to post amplifier 175, 185, which compensates for any additional losses due to the drop, RBF and add. The output of the post amplifier is coupled to line 176, 186, which continues to the next node (e.g., east or west terminal, OLA, OADM, and the like) in the transmission path as is known in the art.
However, the bandwidth capacity of the lines (e.g., fiber pairs) connecting the nodes/terminals often is greater than the bandwidth demand. Accordingly, reducing the number of expensive components, such as optical line amplifiers, can improve the system cost and utilization of the existing infrastructure. Scaling equipment costs to demand are important considerations for service providers, network managers and equipment suppliers.